Manley TAPE HEAD PREAMPLIFIERS - Manual (Page 13)

REPLACING TUBES
How long will these tubes last? We can't say for sure. Some die prematurely and some tubes last
more than 30 years. The average for the tubes in the Manley Tape Head Preamps seems to be 4 to 5
years depending on useage. As with all tubes, their quality degrades with age. This is due to
decreasing cathode emission, a natural process found in all tubes.
How can I tell when I need to replace them? The preamp tubes can become noisy (hiss) or the
preamplifier may exhibit audible distortion; substituting known good tubes is the best way find the
bad one. All tubes are "microphonic" to some extent- that is, they will make ringing noises through
the speakers when tapped or vibrated. Here again, substitution will detrmine which one is excessive.
Obviously, any tube that is totally dark inside while powered up or is cold to the touch (careful!) is
defective. Most tubes have a silvery coating deposited on some area inside the glass bottle. If this
has turned white (compare to another tube), then the tube has lost vacuum (or gained air!) and is
definitely bad. Replace at once- don't turn the preamp on.
Do I need to replace them all at once? No, at least not with these preamps. Some tube amps do
require that if one tube has to be replaced that a complete matched set put in but with these preamps,
you only need replace the offending tube.
Does the "sound" of the amp change as the tube ages? Yes, but not very much. It is just the tubes
and they can be replaced. It is not like big guitar amps where tubes are replaced every 6 months for
reasons of "tone". We run the tubes quite conservatively which allows a very long life and less
change between old and new tubes. This is where that 4 to 5 years of use comes from. You may
notice an improvement between tubes this old and new tubes depending on how critical you are.
Keep in mind the sound of new tubes changes most in the first weeks of use before they can be
considered "broken in". At first the sound may be a little "tight" and "direct" like some people we
know.
Is it difficult to replace a tube? Yes, if you have trouble replacing light bulbs. It is super easy. Turn
off the power. Just let the preamp cool a few minutes so that you don't burn your pinkies. It helps to
wiggle the tube gently rather than pulling it out straight. Even if you don't consider yourself
"technical" you probably have more technical ability than your parents and they used to fix the
family TV set by taking out the tubes and putting them on the tube tester at the local pharmacy. It is
almost as easy to re-insert a tube. Just make sure it is correctly lined up with the socket and you dont
bend a pin. You can wiggle it in too. If you had a solid state amp, it would be an unlikely repair. You
would have to open it up, diagnose the bad transistors and burnt resistors, de-solder, find
replacements (good luck) re-solder, and hold your breath as you turn it on. Or you could send it
back, be without music for a few weeks, pay for service by the hour and get real upset when it fries
again. If one transistor goes the system is dead, not so with power tubes, just limping. If you need a
tube or set of tubes Manley will be happy to sell you some (selected ones ) at a good price and if you
prefer to sent the unit back for repair or adjustment, our warranty covers about everything except
tubes (6 mo. only) and abuse and we handle ground shipping back to you - usually the same week.
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